Poster: Long Distance Transport

Abs # 413: Species-specific and Developmental Regulation of the Long-distance Translocation of GAI mRNA.

Presenter:	Haywood, Valerie , vhaywood@ucdavis.edu
Authors	Haywood, Valerie  (A)   Lucas, William J. (A)
Affiliations:	(A): University of California

The phloem tissue of higher plants has been shown to contain a large population of signaling molecules, implicating the phloem as a long-distance information delivery system. In addition to hormones and proteins, the phloem has recently been shown to contain a heterogeneous population of RNA molecules, suggesting a novel mechanism by which plants use the phloem to transport RNA in order to regulate developmental processes. To investigate this possibility, we have chosen to examine the developmental effects of two highly related (~85%) RNA molecules previously found in the phloem of pumpkin. Cucurbita maxima GAI (CmGAI-P) and CmGAIP-B were chosen based on their high homology (~80%) to the putative transcription factors, Gibberellic Acid Insensitive (GAI) and Repressor of ga1-3 (RGA) from Arabidopsis thaliana. Grafting experiments demonstrate that, while CmGAI-P and CmGAIP-B transcripts are translocated in the phloem, transcripts from the Arabidopsis GAI and RGA homologues are not, suggesting species-specific regulation of long-distance mRNA translocation. However, as the tissues used for grafting differ in developmental stages (i.e vegetative stem tissue used for pumpkin grafts vs. reproductive inflorescence tissue used for Arabidopsis grafts), the possibility also exists that RNA entry into and translocation in the phloem are regulated by an RNA surveillance mechanism (1). This putative RNA surveillance field (SurF) could actively monitor and control the RNA species in the phloem in order to coordinate developmental and physiological events. Experiments aimed at testing these hypotheses will be presented. ¹Haywood et al. (2002). Plant Cell 14 , S303-S325.